It is well known to provide copier devices with variable imaging ratio lens mechanism to provide for image enlargement and reduction. Also devices are well known for changing the focal length of lenses both in photographic as well as copying machines. For example, in U.S. Pat. No. 4,107,714 a means is described for changing the focal length of the lens based on the movement of the lens itself.
In that device, the focal length is changed by means of a toothed ring on the lens which is driven by a rack and pinion mechanism. The rack is held in contact with a guide bar by spring pressure so that on movement of the lens the rack performs a translatory movement depending upon the profile of the guide bar. The translatory movement of the rack is then converted by means of the pinion into a rotation of the toothed ring on the lens. This provides a fixed transmission ratio in the system for changing the focal length, so that there is a rectilinear relationship between the lens movement and the focal length change.
However, when systems of this type are mass produced problems often arise which do not permit the lens to obtain optimum sharpness. Normally, these problems are a result of tolerances in the system components, even within the permitted tolerance limits. Accordingly, it is the object of the present invention to provide a copying machine which offers the facility of respectively so adjusting and correcting the rectilinear relationship between the lens movement and the change of the focal length, within a reasonable tolerance range, that a sharp image can always be obtained in the image plane.